The type of heat pipes I am talking about are wrapped around a cooling coil, they drop the temperature of the incoming air making the cooling coil more efficient at removing moisture, then the outgoing air is reheated by the heat pipe changing the phase back of the refrigerant.
These have no effect on heating. They require a temperature difference across the cooling coil to work. This form of energy recovery is useful in 100% outside air situations where you can't recovery energy from the exhaust air stream. Either because it is corrosive or contaminated, broken into many small amounts, or just too difficult to get the two air streams cose to one another.